It has been known for thousands of years that there is a tremendous amount of power in a flowing body of water such as a river or even a small stream or creek. This power often manifests itself in a destructive manner, as is evident during periods of heavy rain and flooding. However, when a flowing body of water is properly controlled, this power can be utilized in a beneficial manner.
In determining the most effective way to utilize the power in a flowing body of water in a beneficial manner, a crucial problem exists: how does one utilize this power in an economical and practical way? In finding a solution to this problem, three variables become important: (1) the volume of water available; (2) the velocity, or current, of the water; and (3) the difference in elevation between the high and low points in the body of water, commonly known as the head. These three variables are important from a power production standpoint because the velocity of the water represents the kinetic energy of the water, while the volume of the water available, in combination with the head of the water, represents the potential energy of the water. By increasing the velocity of the water, the kinetic energy of the water is increased. By increasing the volume of the water available and/or the head of the water, the potential energy of the water is increased.
A large-scale permanent dam is a structure capable of increasing the value of all three variables. This type of dam increases both the volume of water available and the head of the water by impeding the normal downstream path of the flowing water and increasing the level of the water on the upstream side of the dam. Subsequently, as the volume of water flows under pressure through to the power generating turbines typically associated with such a dam, the kinetic energy of the water increases due to the increase in velocity of the water.
In addition to producing power, a large-scale permanent dam also produces effects on the surrounding geographical area, both economically and environmentally. Economically, a large scale dam, such as the Hoover Dam or one of the many dams built by the Tennessee Valley Authority, is capable of satisfying the energy needs of an entire town or city. A large-scale dam also stimulates local economies by creating construction and energy related jobs. Environmentally, this type of dam reshapes the surrounding landscape by controlling seasonal flooding and by often providing otherwise dry, arid regions with a constant and abundant supply of water.
A large-scale permanent dam also has associated drawbacks, both economically and environmentally. Economically, this type of dam is costly because large tracts of low lying land upstream from this dam must be bought before being flooded. Also, large amounts of concrete, steel and other costly materials must be used in the construction of the dam. Land downstream from the dam may suffer due to the regulated water supply, especially during extremely dry periods. Further, maintenance of these often mammoth structures is costly. Environmentally, dams often upset the "natural order" of the surrounding region. For example, migratory species of fish such as salmon often are permanently incapable of returning to their spawning beds once a permanent dam is built to impede a river. Prime wildlife habitat is often lost as the land upstream from the dam is flooded.
In many cases, these aforementioned drawbacks are overcome by economies of scale. Through government funding and construction by such entities as the Army Corps of Engineers, the benefits associated with a large scale dam more often than not outweigh the drawbacks.
However, many farmers, landowners and other individuals often have a need to produce power from a flowing body of water on a much smaller scale and without the capability of overcoming the aforementioned economic and environmental drawbacks through economies of scale. The specific power needs of these individuals are small enough so that a large scale permanent dam is not needed or is not desired. Thus, the need exists for a structure capable of generating power on a smaller scale without the associated economic and environmental drawbacks associated with a large scale permanent dam.
To fulfill this need, smaller semi-permanent dams have been built that utilize water wheels for generating power from a flowing body of water. These dams utilize water wheels in place of the turbines associated with the large scale permanent dams. The water wheels are especially useful for producing power in smaller moving bodies of water that would otherwise not be utilized as power sources due to the small size of the bodies of water.
A water wheel mounted on one of these smaller dams generates power as flowing water rotates the wheel. A wheel is typically comprised of several spokes emanating from a center axis. Troughs are located on the outer circumference of the wheel to cause the wheel to come into operative contact with moving water. The wheel is mounted on an axle which is attached to a dam at a location that enables flowing water to rotate the wheel and thus generate power. This flowing water can rotate the wheel in one of two ways. First, water falls, due to the force of gravity, onto the troughs of the wheel, causing the wheel to rotate about its center axis. Second, water having a strong current rotates the wheel as the water flows into contact with the troughs and underneath the bottom of the wheel. In both ways, the rotating wheel may power a generator or other power generating or power consuming machinery.
There are three common prior art water wheel designs. The three designs are the overshot, the undershot and the breast wheel designs (see FIGS. 1A-1C). Each of the three designs is most efficient in a particular water level or at a particular water velocity. With the overshot design, the water level is allowed to build up behind the dam to the top of the wheel. Once water reaches the top of the wheel, it flows over the top of the wheel, coming into contact with the troughs of the wheel and causing the wheel to rotate in a clockwise direction (see FIG. 1A). With the wheel of the undershot design, water flows under the wheel at a level high enough for the flowing water to engage the troughs of the wheel and rotate the wheel from the bottom in a counterclockwise direction (see FIG. 1C). With a water wheel of the breast wheel design, the dam impedes water until the water reaches a level intermediate the top and bottom of the water wheel. A water wheel of the breast wheel design is rotated in a counterclockwise direction by a combination of the downstream velocity of the water and the gravitational effect of the water falling from a high upstream point to a low downstream point (see FIG. 1B).
Consequently, the water wheels of the overshot and breast wheel designs are the most efficient in a moving body of water having little velocity or low volume. In these designs, a dam impedes the water, thus raising the level of the water and increasing the head and potential energy of the water. As the water is released over the dam, the potential energy turns into kinetic energy, which in turn is transferred to the water wheel.
The water wheel of the undershot design is most efficient when the velocity of the water is high. If the water is impeded as in the overshot design, flooding can possibly occur due to the already existing high water volume. Similarly, the head of the water need not be increased when the water velocity is high. Power is more efficiently produced from the fast moving water as the water flows through the underside of, and into moving contact with, the troughs on the outer circumference of the water wheel.
Others have utilized certain of these water wheel designs in combination with small scale dams to produce power from flowing bodies of water.
Crow, U.S. Pat. No. 873,845, discloses a portable dam that develops power by utilizing the force or energy of a stream. A diversion assembly comprised of pontoons and vertical rods is positioned to dam a stream. This assembly is placed across the stream to divert a portion or substantially all of the water to one of the shores where it is passed through a raceway. Waterwheels of the undershot design are positioned within this raceway at the downstream end thereof to generate power from the current of the stream. Thus, this movable dam must work outside of the physical boundaries of the river bank in order to be effective.
Wright, U.S. Pat. No. 4,270,056, discloses an undershot current motor wherein a horizontal drive shaft is mounted on floats moored or anchored in moving water. The drive shaft has at least two sets of three-bladed paddle assemblies. The blades generate power through contact with the moving water. The invention also includes a pulley and counterweight system for raising and lowering the floats of the system during changes in the elevation of the water. This undershot wheel design is entirely dependent upon existing water level.
Loreto, U.S. Pat. No. 4,973,856, discloses a hydroelectric generator system that uses a breast wheel design. In this system, water from a stream enters an inflow structure that is placed in the stream. The inflow structure includes lateral walls, overflow openings for discharging excess water when the water level is high, and a step located between the lateral walls that gives the runner breast wheel characteristics. The device specifically defines a runner with blades. The water flows downwardly through an inflow opening in order to produce rotation of the runner. The step cooperates with the runner to effect operation of the breast wheels. The runner is rotatably positioned on a shaft downstream from the step between the two lateral walls. Water flows downwardly through an inflow opening in the step and produces rotation of the runner due to the weight of the water that is accumulated in spaces between the blades of the runner.
Certain drawbacks exist with these aforementioned water wheels. Water wheels are often used in smaller rivers and streams that typically experience significant fluctuation in water level due to various factors often linked to the geographical surroundings. This fluctuation in water level is particularly common in certain areas of the country. For example, in the Midwest United States, land is often left barren for months at a time after crops are harvested. This barren land, having little or no vegetation, can only absorb a limited amount of water during periods of heavy rain. Similarly, in the Southeastern and Pacific Northwest regions of the United States, land that has been deforested by companies in the paper industry can only absorb a limited amount of water during heavy rain. Thus, the smaller rivers and streams running through these areas often exhibit significant fluctuation in water levels due to the tremendous amount of runoff water flowing into the rivers and streams during periods of heavy rain. Conventional water wheels lack the capability of being adjusted to maximize the efficiency of the wheel in response to these changing water levels. The water wheels discussed in Crow and Loreto, for example, are specifically designed for use in a particular stream at a particular location with a specific water level. This leaves little room for adaptability to conform to changing conditions. Power is not necessarily efficiently generated from moving water by such rigidly designed structures.
Also, the system discussed in Wright may be adjustable as a whole to adapt to changes in water level. However, the water wheel itself is not adjustable; the entire platform on which the wheel is mounted must be moved upwardly or downwardly as water supply varies, thus maintaining the wheel in an undershot mode. While the platform is able to provide vertical movement of the wheel, the assembly is not readily moved from its initial location.
While these devices address many of the needs for production of energy on smaller streams and rivers, the devices do not provide flexibility in adapting to changing water conditions. Stated more particularly, there is a need in the art for a dam and waterwheel structure that is capable of being moved from one location to another and that is adjustable among overshot, breast and undershot modes of operation to produce power at maximum efficiency in response to available water quantity and flow.